Those Doctor Who viewers hoping for more in regards to last week’s mind-breaking revelations will likely be disappointed tonight, as Praxeus is content to simply weave its own tale and leave the arc plot well alone for now. However, their disappointment should soon wane, as the result is an enjoyable standalone story that sees Doctor and friends investigate three inter-linked mysteries across just as many continents.

Like Orphan 55 from earlier this series, Praxeus is an ecological parable, this time taking a shot at our planet’s alarming amount of plastic waste. Within the story, alien scientists weaponise plastic pollution from the world’s oceans in order to combat a deadly virus (by using humans and birds as guinea pigs in the process). The result is a wonderful Doctor Who conceit, as real science feeds into the fiction. Unlike Orphan 55, the eco-message isn’t shoehorned in at the last minute as an afterthought, the plot instead building neatly to a clever reveal that is explained without any need for rushed or awkward speeches.

Pete McTighe and Chris Chibnall deliver a bracing, fast-paced sprint of an episode – the plotting is particular adept at keeping the momentum going, even during the dialogue heavy exposition. There’s some wonderful sequences scattered throughout the episode too, with the inter-continental landscapes making for gorgeous visuals and the swarms of infected birds attacking our heroes resulting in some truly ominous imagery (all down to excellent direction from Jamie Magnus Stone). The Birds are an especially nice touch – Doctor Who always does a great job of taking the familiar, the safe, and the everyday and turning it into something terrifying, and this episode is no exception to that rule. Lots of children will likely be too afraid to chase pigeons in the high street come Monday!

Primary guest stars Matthew McNulty and Warren Brown are excellent in their respective roles as a mismatched couple (an astronaut and his emotionally closed-off copper husband) who find themselves swamped up in the entire adventure, and lend a nice bit of heart to the zippy plot. It’s particularly nice to see such normal representation of an LGBT relationship in a family show on prime-time telly as well, instead of it just being referenced in passing through dialogue or employed as a punchline.

The other guest characters are far less engaging though, especially Joana Borja‘s travel blogger Gabriela (through no fault of Borja, who tries her best with such an unnecessarily insufferable character). Gabriela serves no purpose here, whilst her one-note character comes across as horribly self-absorbed, even after her best friend’s death. Molly Harris fares no better either, and is extremely underused as the villain of the piece. There’s too many guest characters here, which does somewhat hamper proceedings when you try and juggle them alongside the Doctor and three underdeveloped companions.

Herein lies the only major fault with Praxeus, in that it tries to pack too much in. There’s some slightly odd plot holes scattered throughout the episode that go unexplained (Adam’s text message), and the climactic scenes take a lot of liberties with logic – can Jake (Warren Brown) really fly a spaceship that easily with no training?! The breakneck pacing is welcome and keeps things from getting saggy or dull, but this is unfortunatly at the expense of some major characters and plot threads.

All said and done though, Praxeus is another feather in Series 12’s cap, thanks to some brilliant direction, lovely guest turns and brisk plotting that holds clever and relevant ideas at it’s core. Whilst it lacks the shock factor of last week’s episode, it’s nice to see the show can still serve up a decent standalone story in and amongst all the revelatory twists of this season.

Doctor Who returns to BBC One next Sunday. Be sure to check out our Series Blog and join us for our verdict of Episode 7.